An exemplary ash-free coal production method is one described in Patent literature (PTL) 1. The ash-free coal production method described in PTL 1 produces an ash-free coal by mixing coal with a solvent to prepare a slurry; heating the obtained slurry to extract a solvent-soluble coal component; separating the slurry containing the extracted coal component into a solution containing the solvent-soluble coal component and a solvent-insoluble-component-enriched fluid containing a solvent-insoluble coal component; and recovering the solvent from the separated solution. PTL 1 refers to spray drying as a process of recovering the solvent to give the ash-free coal.
The spray drying described in PTL 1 allows an organic substance and an inorganic substance in the ash-free coal to precipitate separately and enables easy removal of a fine inorganic substance and a metal component from the solution containing the solvent-soluble coal component, where the inorganic substance is mixed in the solution in a small amount, and the metal component is dissolved in the solvent.